Temperature sensitive goods/products are generally transported through logistics channels in shipping containers that are constructed using insulated materials and heat transfer elements (HTE). These temperature sensitive products include high-value foodstuffs, live cultures, laboratory samples, raw materials and biological products such as blood products, testing reagents, vaccines and a variety of biopharmaceuticals that treat hormone deficiencies, virus infections and cancers. In particular, biological products have storage conditions that are registered with the Federal Drug Administration (FDA), the U.S. Department of Agriculture (USDA) and other domestic and foreign regulatory agencies. Regulatory agencies oversee the safe transport of temperature sensitive products to ensure these products' diagnostic accuracy and therapeutic viability.
In recent years, regulatory agencies have increased their enforcement of regulations concerning the safe transport of temperature sensitive products. Accordingly, shippers of temperature sensitive products have had to verify the performance of their SC systems and many have had to make costly improvements to their SC systems to ensure compliance with these regulations.
SC systems generally use insulating materials to isolate payload from ambient temperature conditions. Insulating materials are materials that have relatively high heat resistance values, or R-values. Typical insulating materials found in SCs are expanded polystyrene foam (EPS), polyurethane foams (PU) and vacuum insulated panels (VIP). Less typically, other materials are used that are generally not thought of as insulating, but which have high R-values; materials like corrugated paperboard, bubble wrap, wood, cellulous pulp, fiberboard and the like. It should be noted here that all materials, including conducting materials, resist the transfer of heat, and therefore all materials have an R-value and could play a limited insulative role in the heat transfer processes discussed herein.
Thermal insulation is used in the construction of SCs to isolate payloads from ambient conditions, while HTEs are used within a closed SC system to regulate the transfer of heat from the payload. HTEs most typically used include ice, dry ice, gel packs, foam refrigerant, endothermic phase change materials, exothermic phase change materials and the like.
Conventional passive container systems transfer heat by conduction between HTEs and the payload. Conduction is a direct heat transfer method that relies on direct contact between the surfaces of two bodies with differing temperatures. In many conduction-based heat transfer systems insulating materials, or buffering materials, are placed between the HTE and the payload. Buffering materials may typically include chilled secondary HTE or a variety of insulating materials or both. Buffering materials function by resisting the transfer of heat, which reduces the efficiency of the heat transfer process. The primary HTE thus buffered now forms a less efficient heat transfer system that will transfer heat directly by conduction through the buffering materials.
Preferred payload temperature is adjusted in typical conduction-based heat transfer systems by adjusting the surface-to-surface contact between the payload and the buffering materials, and by adjusting the surface-to-surface contact between the buffering materials and the HTE. Shipping duration is adjusted in typical conduction-based heat transfer systems by adjusting the mass and composition of HTE, and adjusting the R-value of both the buffering materials and the SC materials.
In better conduction-based systems the phasing temperature of the HTE is precisely calibrated to match the preferred payload temperature, allowing the HTE to be in direct contact with the payload without a buffering material between. These improved HTEs are generally much more expensive per pound than conventional HTEs, generally absorb less heat than conventional HTEs, generally require expensive high-performance SC insulations, and generally require a larger HTE mass, all of which adds weight, cost and complexity to the SC systems and generally returns limited performance and duration improvements.
When smaller payloads are shipped in conduction-based SC systems the payload surface area available for surface-to-surface-contact is limited, and so the heat transfer system is typically placed above and/or below the payload in contact with a single payload surface. This configuration supplies uneven heat transfer due to the limited contact between the heat transfer system and the payload. When larger payloads are shipped in conduction-based SC systems the payload surface area available for surface-to-surface contact is more generous, and so the heat transfer system can be expanded across additional payload surfaces. This configuration supplies greater, more even heat transfer due to the greater contact between the heat transfer system and the payload. However, the corresponding increase in HTE and/or buffering materials required to increase the contact between the heat transfer system and the payload adds weight, complexity and cost to the SC system. As complexity and weight increase so too does the risk that the HTE and buffering materials in the heat transfer system will dislodge and migrate during shipment causing the heat transfer system to become unbalanced resulting in system failure.
Recent attempts to improve SC system design have been met with mixed success. In one example, a SC is disclosed whereby refrigerant is placed on a tray, separate from the payload. See, e.g. U.S. Pat. No. 4,576,017 to Combs et al., incorporated herein by reference. While '017 attempts to minimize the problems associated with putting buffered refrigerant in direct contact with the payload, the refrigerant tray itself has an R-value and acts as a buffering material through which heat must transfer by conduction, making the heat transfer process inefficient. In practical terms, to compensate for the reduced efficiency introduced by the refrigerant tray's resistance, '017 requires the use of more refrigerant to achieve equivalent efficiency to that of a SC system that does not include a refrigerant tray.
The '017 patent also discloses grooves or channels or protrusions that attempt to increase the air flow around the payload. However, the placement of these structures provide sufficient contact between the surface area of the payload and the surface area of the structures themselves, deleteriously reducing air flow around critical parts of the payload, leading to uneven cooling of the payload, especially around the base or bottom of the payload. Furthermore these designs continue to be costly, are difficult to construct, are not scalable, and do not lend themselves to pre-packaging or automated packaging.